With limited freshwater resources, Singapore relies on the sea for an estimated 10 percent of its water supply. Purified at five desalination plants across the island, this stable, weather-independent source is crucial to the nation’s water security strategy. However, the concentrated brine that desalination produces as a byproduct must be carefully managed to avoid disrupting delicate marine ecosystems—a process both costly and energy-intensive.
Yet, according to Yan Liu and Jiajian Gao, Scientists at A*STAR’s Institute of Sustainability for Chemicals, Energy and Environment (ISCE2), this salty solution holds untapped potential for environmental benefits. Metal ions in brine, like magnesium and calcium, can react with carbon dioxide (CO2) to form stable carbonate minerals, not only capturing greenhouse gases but also creating valuable industrial resources.
“By recovering minerals with CO2 as carbonates, carbon abatement can be achieved,” said Liu. “This aligns with Singapore's commitment to sustainability and supports its goal of net zero carbon emissions by 2050.”
However, one major difficulty when pairing brine mineral recovery and carbon capture is that products can be inconsistent. Brine's diverse metal ion content can create a mix of different precipitates, and multiple factors like pH, temperature and pressure can also affect the chemical reactions involved, altering the types of minerals produced.
To shed light on the area, Liu, Gao and colleagues explored how changes in two factors—CO2 concentration and alkalinity (as hydroxide, or OH− ions)—affected the chemical reactions that form carbonate minerals, such as calcite and brucite, from CO2 captured in brine. Calcite is a key ingredient for construction materials; brucite likewise for thermal insulation.
“These two factors were chosen specifically because their optimisation can enhance the rate and efficiency of mineral recovery,” said Liu. “By understanding and controlling them, we can improve the overall sustainability and economic viability of the CO2 mineralisation process.”
The team used two advanced simulation software modules: Visual MINTEQ to do the calculations behind the mineral precipitation process, and PHREEQC to conduct thermodynamic simulations. Optimal reaction conditions found by the modules were then validated with electrochemical experiments using brine solutions, which involved passing an electric current through brine to generate OH− ions.
They reported that higher CO2 levels relative to OH− ions favoured calcite formation, while brucite formation was suppressed. They also found that the phase composition of the precipitated minerals (i.e., the proportions of each mineral type) could be precisely controlled by adjusting the electric current and gas flow rates during electrochemical process.
“This simulation-based approach, combined with electrochemical results, offers a new way to control mineral composition during CO2 mineralisation in brine solutions,” said Liu.
Based on their findings, the researchers have filed several patents and are currently working with industry partners Pan United Corporation Ltd to improve mineral recovery efficiency and develop novel cement alternatives.
The A*STAR-affiliated researchers contributing to this research are from the Institute of Sustainability for Chemicals, Energy and Environment (ISCE2).
